The Low Dimensional Fermiology on the Organic Superconductors (TMTSF) 2 X

1. The Low Dimensional Fermiology on the Organic Superconductors (TMTSF)2X Ok Hee Chung Department of Physics, Sunchon University 2005.8.9

2. Contents Structure of (TMTSF)2X Q1D electronic system P-T-H phase diagram of (TMTSF)2X Dimensional Effects: RO, 1D & 2D ADMRO, SdH-Osc Role of anion X-(PF6, ClO4, FSO3) Conclusions

3. (TMTSF)2X:Bechgaard Salts TMTSF-molecule: TetraMethylTetraSelenaFulvalene, (CH3)4C6Se4 PF6 , AsF6 : Centrosymmetric (octahedral) ClO4 , ReO4 : Noncentrosymmetric (tetrahedral) . FSO3 : Tetrahedral-like: electric dipole moment NO3: Planar • Anions(X-)

4. Unit cell of (TMTSF)2X Triclinic Structure(abc, )

5. Structure of (TMTSF)2PF6 a c ta: tb: tc = 100: 1: 0.3 meV ⇒ Q1D system (σa : σb : σc = 10000 : 1 : 0.1)

6. Fermi surfaces of various dimensions Q1D energy dispersion (k)=vF(|kx|-kF)-2tbcos(kyb)-2tccos(kzc)

7. Ground States of the Q1D metals T 0 1D insulator CDW or SDW 1D metal No long range interaction Lattice modulation

8. Peierls Instability of 1D metals Metallic state (high T) NO long range order interactions CDW(SDW) state (low T)

9. Nesting of Q1D FS Nesting vector kP=(2kF, /b, 0) New Brillouin Zone Opening of Peierls gap 2 at kF

10. Fermi surface and nesting of electron systems of various dimensions Only for the one-dimensional (1D) case the nesting with respect to the translation |kp|=2kF is perfect. So, the 1D system undertakes metal-insulator transition as T goes zero.

11. Ground states of (TMTSF)2X

12. Universal P-T phase diagram

13. H-field along the c*-axis ⇒

14. H-field along the c*-axis A cascade of FISDW transitions The field flattens the warped FS ⇒ Restoring 1-D ; Field Induced Spin Density Wave (FISDW) Nesting vector : H-dependent quantized

15. 3-D Phase diagram

16. Quantum Hall effects Magnetic oscillations in MR

17. Rapid Oscillations in (TMTSF)2ClO4 F0= 260 T (~2% of the 1st BZ) SdH-osc? Weird T- & H-dependence Two kinds of oscillations Not SdH ⇒ No closed electronic orbit In Q1D .

18. A new H-T phase diagram of(TMTSF)2ClO4

19. (TMTSF)2ClO4 Observed Phenomena • Superconductivity (Tc=1.4 K) with anion ordering at T=24 K (dT/dt ~0.5 K/min) @ P=0 kbar 2. A cascade of FISDW transitions 3. Quantum Hall effects (change of sign of Hall voltage) 4. Two kinds of magnetic quantum oscillations in MR and magnetization (so called Rapid oscillations) F = 260 T 5. Angular Dependent MagnetoResistance Oscillations –Lebed type oscillations (Q1D FS) 6. Exotic High field state

20. In a titlted field; H=(0,Hsin, Hcos ) Lebed- oscillations magic angles {tan = (n/m)b’/c* } ; commensurate effects

21. Commensurate Conditions:magic angle

22. (TMTSF)2PF6 1-D ADMRO: Lebed Osc.

23. Rotation in the ac-plane tb 0.012 eV, tc=~tb/15

24. (TMTSF)2ClO4, (TMTSF)2PF6 • Q1D ADMRO: Lebed-Oscillation • Due to only the geometry of the lattice. • No information on the Fermi surface

25. (TMTSF)2FSO3 5 kbar< P < 12kbar 1.SC with Tc=~ 3K 2. NO FISDW transition upto 35 T 3. osc. with F=130 T

26. Conventional SdH-osc. in (TMTSF)2FSO3 the Lifshitz-Kosevich formula

27. Shubnikov de Haas Oscillations • Applying Onsager relation (F = (h/4π2e)S). • S = 1.248×1014 cm.-2 for F0 = 131 T : (~ 1.6% of SFBZ in the ab) • Fit to the L-K formula mc= 1.4 mo, TD= 2.2 K

28. ADMRO of (TMTSF)2FSO3 is not Lebed-type.

29. Q2D-Fermi surface Yamaji resonance ckF tan  =(N -¼)

30. kF=0.14 A-1

31. SdH-osc. in titled fields

32. Freq vs.  Amp. vs. 

33. 2N=gmb0/cosQN+1

34. spin-splitting factor Rs=cos(pgb/2) in L-K formula

37. Final shape of Fermi surface of (TMTSF)2FSO3

38. Conclusions X=PF6, ClO4 Q1D electronic system X=FSO3 Q2D electronic system Why? Depends on Anion Symmetry?

39. (TMTSF)2ClO4 under pressure